The present invention relates to an imaging apparatus including solid imaging devices.
In imaging devices made of silicon, an electrode voltage such as substrate voltage is varied to change the saturation characteristic of photodiodes (PD). A positive pulse voltage is applied to an overflow drain (OD) of substrate (Sub) to thereby sweep away electric charges of photodiodes. FIT-CCD (Frame Interline Transfer—Charge-Coupled Device) and IT-CCD (Interline Transfer—Charge-Coupled Device) among CCD's (Charge-Coupled Devices) have overflow drain formed by substrate and named vertical-type overflow drain (refer to CCD area image sensor, 39781AE Panasonic Inc.)
FIG. 5B is a block diagram schematically illustrating a conventional imaging apparatus 501. An imaging part 503 of FIG. 5B includes IT-CCD, a vertical transfer drive part having timing generator (TG), sweeping-away function of overflow drain (OD) and reading function, a correlated double sampling (CDS) for removing noise, a dark-current correction and automatic gain control (AGC) amplifier circuit, an analog-to-digital converter (ADC) for converting analog signal into digital image signal Vi, a timing generator (TG) for horizontal transfer, a timing generator (TG) for reset of voltage conversion, a timing generator (TG) for correlated double sampling (CDS), a timing generator (TG) for correction of dark current, a timing generator (TG) for automatic gain control (AGC), a timing generator (TG) for analog-to-digital converter (ADC) and one CCD having on-chip color filter or color separation optical system and three CCD's. Various forms of the plural timing generators are considered as the case where the plural timing generators are dispersed or divided for each of functions and the case where the plural timing generators are integrated into one timing generator, although objects to be timing controlled are as described above and timing pulses thereof are divided into pulses repeated at horizontal period and at vertical period. Part or all of the functions described above are sometimes integrated to use an integrated circuit (IC) named AFE (Analog Front End), although there is no difference in realized functions. Incident light focused by a lens 502 becomes image signal in the imaging part 503 and the image signal is processed by an image signal processing part 505 having scanning line number conversion function and chromatic magnification aberration correction function. The imaging part 503 and the image signal processing part 505 are controlled by CPU (Central Processing Unit) 504 (refer to JP-A-2008-206030).
The imaging part 503 includes timing generator (TG) 506. FIG. 8B is a block diagram schematically illustrating an example of the timing generator contained in the imaging part of the conventional imaging apparatus.
A clock counter 801 counts clocks for performing horizontal input sampling to output a horizontal count value. A comparator 802 compares a maximum value of horizontal input sampling with the horizontal count value and when the maximum value is coincident with the horizontal count value, the comparator 802 outputs horizontal reset and vertical count-up signal. The clock counter 801 is reset by the horizontal reset and vertical count-up signal of the comparator 802 to repeat counting of horizontal periods.
A line counter 803 counts up clocks having horizontal reset and vertical count-up signal to output a vertical count value. A comparator 804 compares a maximum value in vertical line with the vertical count value and when both values are coincident with each other, the comparator outputs vertical maximum line flag signal. An AND circuit 805 calculates AND or logical product of the vertical maximum line flag signal and the horizontal reset and vertical count-up signal and outputs a vertical reset signal. The line counter 803 is reset by the vertical reset signal of the AND circuit 805 and repeats counting of vertical periods.
A horizontal pulse production circuit 806 produces various horizontal pulses required by CCD in accordance with the horizontal count value. The horizontal pulses correspond to pulses repeated at horizontal period such as horizontal transfer pulse, voltage conversion reset pulse, CDS pulse, dark-current correction clamping pulse, AGC part clamping pulse and ADC horizontal synchronization pulse.
A vertical pulse production circuit 807 produces vertical pulses required by CCD in accordance with the vertical and horizontal count values. The vertical pulses correspond to pulses repeated at vertical period and having horizontal pulse displacement phase such as OD sweeping-away pulse, reading pulse and vertical transfer pulse.
The image signal processing part 505 includes a conversion filter 507 for processing scanning line number conversion and the like. The conversion filter requires repetition of conversion coefficient at each sampling for converting sampling points in horizontal and vertical directions in accordance with relative phase relation of input and output and has a plurality of conversion coefficients. FIG. 9B schematically illustrates the concept of the conversion coefficients based on 0-degree phase contained in the image signal processing part of the conventional imaging apparatus.
A horizontal sample conversion filter 901 is an FIR (Finite Impulse Response) filter which can change conversion coefficient for each clock and multiply conversion coefficient values corresponding to coordinates thereof for a plurality of input pixels within a fixed range and add up them to thereby produce pixel information corresponding to phase center of output sample.
Phase 902 of horizontal conversion coefficient gives conversion coefficient used in filter calculation to the horizontal sample conversion filter 901. The phase 902 of horizontal conversion coefficient contains a plurality of sets of conversion coefficients and gives the sets of conversion coefficients for phase according to value of registration correction set by CPU 504 to the horizontal sample conversion filter 901. Example of contents of numerical values of conversion coefficients is described separately, although kinds of phases provided as the sets of conversion coefficients concerning a point of view of this method are described here.
The plurality of sets of conversion coefficients contained in the phase 902 of horizontal conversion coefficient are schematically illustrated in combination of coordinates 903 of input pixels, phase centers 904 of output samples and relative responses 905 to black and white in unit of input pixels. First, the phase 902 of horizontal conversion coefficient has a set 910 of conversion coefficients of 0-degree phase in which the coordinates 903 of input pixels and the phase center 904 of output sample are coincident. In addition, there are provided the sets of conversion coefficients having different phase centers 904 of output sample and coordinates 903 of input pixels used for registration correction and sampling (scanning line in vertical direction) conversion, although the sets of conversion coefficients are provided as phase appearing successively from 0-degree phase when the phase of input and output is changed in sampling (scanning line in vertical direction) conversion. Here, conversion of input/output of 3 to 4 which is utilized with high frequency and is easy to be explained is taken as an example such as the case where 960 pixels are converted into 1280 pixels and the case where 1440 pixels are converted into 1920 pixels. 4 kinds of phases are required every 90 degrees from 0-degree phase and accordingly there are provided a set 911 of conversion coefficients of 90-degree phase, a set 912 of conversion coefficients of 180-degree phase and a set 913 of conversion coefficients of 270-degree phase.
A correlation diagram 906 of conversion of input/output of 3 to 4 in the horizontal sample conversion filter 901 shows that the sets of conversion coefficients contained in the phase 902 of horizontal conversion coefficient can be converted repeatedly for four kinds every output clock. 0-degree phase that amplitude of relative response to black and white is maximum and 180-degree phase that amplitude does not exist at all and is smoothed exist together in the repeated conversion. Accordingly, moiré (flicker and jitter in vertical direction) or the like is liable to be caused to degrade the image quality and the conversion characteristic of filter is required to be approximated to 180-degree phase having the least amplitude in order to approximate the conversion characteristic of filter for improvement of the above defects, so that the merit of the 0-degree phase having maximum amplitude cannot be utilized effectively to reduce the resolution.
A vertical scanning line conversion filter 921 is an FIR filter which can change conversion coefficient for each scanning line and multiply conversion coefficient values corresponding to coordinates thereof for a plurality of input pixels within a fixed range and add up them to thereby produce pixel information corresponding to phase center of output scanning lines.
Phase 922 of vertical conversion coefficient gives conversion coefficient used in filter calculation to the vertical scanning line conversion filter 921. The phase 922 of vertical conversion coefficient contains a plurality of sets of conversion coefficients and gives the sets of conversion coefficients for phase according to value of registration correction set by CPU 504 to the vertical scanning line conversion filter 921. This portion is different in that directivity is horizontal or vertical and coefficient is changed over every clock or every scanning line and accordingly detailed description thereof is omitted.
Filter coefficient is reversed every field in interlacing and 0-degree phase and 180-degree phase appear in the same space coordinates alternately, so that moiré causes flicker and jitter at edge.